Is that what sprinkling with holy water is about, then, FS, purification before entering the place of worship?

Yes and no. (How's that for a typical theological answer?) When sprinkling with holy water occurs as part of the entrance rite (salutation, song of praise, collect of the day), it can certainly be understood as a rite of purification before (or at the beginning of) worship. When it occurs later in the liturgy (e.g. during the recitation of the Creed), then it functions as a reminder of baptism and the renewal of baptismal vows. There is yet a third function, at some liturgies, where it is a form of blessing.

And one needs to be careful about saying too much about what a symbol "means" in that really good symbols are loaded with more meaning than can be contained in so small a box.